Station, a passive portable object and apparatus for the remote exchange of information between the passive portable object and the station

ABSTRACT

Apparatus for the exchange of information by electromagnetic coupling between a passive portable object and a station comprising: first electromagnetic coupling means for the transmission of data between the portable object and the station, and second electromagnetic coupling means independent of the first means for the transfer of energy and a clock signal to the portable object. A filtering circuit is provided on the station side, which behaves as an inductance at the frequency associated with the data transmission and as a high value impedance at the frequency associated with the energy transfer.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention concerns the remote exchange of informationbetween a passive portable object and a station.

In general the term portable object refers to a contactless memory cardor the like, intended for any application suitable for contactlessmemory cards, or an electronic label intended, for example, for theautomated monitoring of objects such as packages. The portable object issaid to be "active" when it comprises an internal energy source (cell orbattery) which supplies the various elements constituting the portableobject. It is said to be "passive" when it contains no internal sourceof power.

2. Description of the Related Art

French patent application FR-A-2 711 440 filed by the applicant on 18Oct. 1993 describes an active portable object exchanging informationwith a distant station via an electromagnetic coupling.

The transmission of information from the portable object to the stationis prompted by the switching of an electronic circuit in the portableobject which causes the phase to vary between an alternating referencevoltage and an alternating voltage at the terminals of the inductiveelement (or antenna) of the station during the inductive coupling of thestation antenna with the inductive element (or antenna) of the portableobject.

In the other direction, the transmission of information from the stationto the portable object is prompted by the switching of the electroniccircuit of the portable object caused when an alternating voltage isinduced in the inductive element of the portable object by theapplication of an alternating signal in the inductive element of thestation.

In practice, during the dialogue phase, the distance between the stationand the portable object varies from 1 to 10 cm.

The present invention addresses the problem of eliminating the internalpower source of the portable object in order to render it autonomous.

An apparatus is already known in which the same alternating signal andthe same antenna are used for the exchange of information and thetransfer of energy.

However, the implementation of data transmission from the station to theportable object requires the use of complex modulation, phase modulationfor example, which requires sophisticated demodulation electronics inthe portable object. Similarly, the electronics must permanently providethe function of clock recovery and energy transfer in the portableobject and cannot use simple modulation, such as all or nothingmodulation. Also, when several stations are close to each other,radio-electric parasitic voltages can disrupt the exchange protocols.

Furthermore, the applicant has found that the antenna emitting theremote supply signal (here the second inductive station element) isliable to interfere with the antenna dedicated to data transmission(here the first inductive station element).

SUMMARY OF THE INVENTION

The present invention presents a solution to these problems.

It concerns an apparatus in which the station comprises

a first generator of a first alternating voltage with a first selectedfrequency and

a first resistive station element with a first terminal linked to thefirst generator and a second terminal.

A series arrangement is linked to the second terminal and has at least afirst inductive station element, a first capacitive station element anda second resistive station element. The series arrangement is able togenerate at its terminals a second alternating voltage.

A station processing means is linked to the first and second terminalsof the first resistive station element and is able to process phasevariations between the first and second alternating voltages.

The portable object comprises

an electronic circuit comprising a first inductive object element and afirst capacitive object element. The circuit is switchable between aninactive state and an active state in which it forms a resonant circuitwith the first inductive station element.

Object processing means are provided which are able to switch theelectronic circuit as a function of the information to be transmitted tothe station. The phase variation between the first and secondalternating voltages induced by this switching enables the stationprocessing means to deduce from this the information thus transmitted tothe station.

In a general definition of the invention, the station further comprises

a second generator of a third alternating voltage with a selected secondfrequency different from the first frequencys.

A second inductive station element is linked to the second generator,independent of the first inductive station element and is able to createa predetermined magnetic field.

The portable object also comprises

a second inductive object element independent of the first inductiveobject element.

A second capacitive object element is linked to the terminals of thesecond inductive object element. The second inductive object element isbeing able to form a tined loop with the second inductive stationelement in order to create at the terminals of the second inductiveobject element an induced alternating supply voltage in the presence ofthe magnetic field created by the second inductive station element.

The station further comprises a filter circuit of the dipole typeinterposed between one of the electrodes of the first capacitive stationelement and one of the terminals of the first inductive station element.The filter circuit is able to behave as an inductance at the firstfrequency and a high value impedance at the second frequency.

Thus, the apparatus according to the invention eliminates the internalenergy source of the portable object and creates a supply voltage withenergy appropriate for supply of the elements constituting the portableobject. It thus allows easier implementation of the energy and datatransfer functions and better protection from interference betweenadjacent stations in relation to an apparatus using the same alternatingsignal and the same antenna for the exchange of information and thetransfer of energy. Moreover, the filter circuit of the station allowscancellation of the interference of the remote supply antenna with theantenna dedicated to the transmission of data.

In practice, the filter circuit comprises an inductive element and acapacitive element connected in parallel and arranged between the firstcapacitive and inductive elements of the station.

According to another characteristic of the invention, the first andsecond inductive station elements have approximately the same geometricdimensions and are superimposed another.

The advantage of such an arrangement is that it is easy to implement inrelation to a particular juxtaposition of one antenna on the other.

Moreover, thanks to such an arrangement of station antennae, it is notnecessary to apply the portable object in a particular geometricrelation with respect to the station. It is sufficient, according to theinvention, simply to use the portable object close to the stationantennae.

In another preferred embodiment of the invention, the portable objectalso comprises clock recovery means linked to the terminals of thesecond inductive object element and able to recover a clock signal fromthe induced alternating supply voltage. The clock signal is intended toset the timing of the elements, of logic or memory type, constitutingthe passive portable object. Advantageously this clock recovery allowselimination of any internal clock device, for example of quartz, in theportable object.

In practice, the portable object also comprises rectifying means linkedto the terminals of the second inductive object element and able torectify the induced alternating supply voltage into a DC supply voltageintended to supply the object processing means.

Preferably the portable object also comprises an energy regulationcircuit linked to the outlet of the rectifying means and able toregulate the induced DC supply voltage as a function of the distancebetween the station and the portable object.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages of the invention will appear in thelight of the detailed description below and the attached drawings inwhich:

FIG. 1 shows diagrammatically an information exchange apparatusassociated with access control according to the prior art;

FIG. 2 shows diagrammatically the information exchange apparatus betweenan active portable object and a station according to the prior art;

FIG. 3 is a diagrammatic representation of the constituent elements ofthe system of energy transfer by induction on the station side accordingto the invention;

FIG. 4 shows diagrammatically the block dedicated to the transmission ofdata in the station described with reference to FIG. 2 and modifiedaccording to the invention;

FIG. 5 is a diagrammatic representation of the essential constituentmeans of the portable object according to the invention; and

FIG. 6 is a diagrammatic representation of the two antennae of theportable object according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

According to FIG. 1, in a particular embodiment of the invention whichis in no way limiting, the portable object 10 is of the memory card typeand the station is a terminal 12 equipped with an inductive gate 14through which a person 16 can pass carrying the memory card 10.

For example, the station may be is an electronic assembly contained in ahousing of selected dimensions. For example, the dimensions so which are40 cm×16 cm with a thickness of 4 cm.

Additionally, the portable object may be, for example, a device withdimensions 8.5 cm×5.4 cm and thickness 0.5 cm. The portable object isintended to be presented in front of the station. This portable objectmay achieve a speed of 1 m/s. During the dialogue phase, the distancebetween the station and the portable object may vary from 1 to 10 cm.

The operation performed on each passage allows the station to read amemory region contained in the portable object and then write to thesame memory region new information sent by the station.

FIG. 2 shows at least in part the apparatus for the exchange ofinformation by electromagnetic coupling between a portable object and astation such as that described in patent application FR-A-2 711 440mentioned above.

In general, station 12 comprises a block 13 dedicated to datatransmission.

Such a block is described in detail in the above patent application, thecontent of which is incorporated herein by reference.

Essentially block 13 comprises:

a first generator GI of a first alternating voltage VEX with a firstselected frequency F1,

a first resistive station element RC with a first terminal B10 linked tothe first generator G1 and a second terminal B20,

a series arrangement linked to the second terminal B20 and having atleast a first inductive station element L1, a first capacitive stationelement C1 and a second resistive station element R1, said arrangementbeing able to generate at its terminals a second alternating voltageVEY,

station processing means (not shown) linked to the first and secondterminals of the first station resistive element RC and able to processthe phase variations between the first and second alternating voltagesVEX,VEY.

For its part, the portable object 10 comprises a block 11 dedicated todata transmission.

This block 11, described in detail in the above patent application,essentially comprises:

an electronic circuit 3 switchable between an inactive state and anactive state in which it forms a resonant circuit with the firstinductive station element L1, and

object processing means 5 able to switch the electronic circuit 3 as afunction of the information to be transmitted to the station, the phasevariation between the first and second alternating voltages induced bythis switching enabling the station processing means to deduce from thissaid information.

The electronic circuit 3 comprises an inductive element L30 and acapacitive element C30.

In a preferred embodiment, the antenna L30 has a value of 9 μH dividedover 8 windings and the capacitor C30 has a value of 61 pF.

The transmission of information from the portable object 10 to thestation 12 is prompted by the switching of the electronic circuit 3 ofthe portable object (by the action of switching means MC) which causesvariation in the phase between the reference alternating voltage VEX andthe alternating voltage VEY at the terminals of the series arrangementL1, C1 and R1 of the station, during the inductive coupling of thestation antenna L1 with the inductive element (or antenna) L30 of theportable object.

In the other direction, the transmission of information from the stationto the portable object is prompted by the switching of the electroniccircuit of the portable object (by the action of switching means MCA)caused when an alternating voltage is induced in the inductive elementL30 of the portable object by application of an alternating signal inthe inductive element L1 of the station.

For example, the generator GI supplies an alternating voltage VEX a peakvoltage of 1.5 volts and with a frequency F1 equal to 6.78 MHz.

An internal power source 7 delivers a DC supply voltage +VDD to theconstituent elements of block 11.

According to the invention, the internal power source of the portableobject which supplies the constituent elements of block 11 is eliminatedthanks to the addition of a system of energy transfer by induction withtwo antennae independent of those dedicated to the transmission of data.

According to FIG. 3, the system of energy transfer by induction is basedon the generation of an alternating supply signal by a second generator(G2) arranged in the station.

In practice, the second generator G2 is an oscillator able to supply analternating signal at frequency F2 different from the first frequency F1dedicated to data transmission, and for example equal to 13.56 MHz.

A second inductive station element (or antenna) L2 is linked to thesecond generator G2 through amplifying means AMP.

The antenna L2 is independent of antenna L1. It creates a magnetic fieldCM2 when conducting a signal of frequency F2.

The two frequencies F1 and F2 differ from each other so as to allowcancellation of the radio-electric interference of the system ensuringthe transfer of energy in the system and ensuring the exchange ofinformation.

The frequency of the radio-electric signal ensuring the transfer ofenergy from the station to the portable object is chosen such that itallows the best yield of energy transmission.

The two antennae L1 and L2 of the station are active, i.e. they eachemit a magnetic field. The intensity of field CM2 emitted by antenna L2ensuring the transfer of energy is substantially greater than theintensity of field CM1 emitted by antenna L1 ensuring the exchange ofinformation.

It should be noted that in the case where several stations are close toeach other, the interference between stations is reduced in relation tocontactless systems with remote supply using a single frequency for thetransfer of energy and the exchange of information.

In general, for a given voltage, the remote supply power is maximum fora minimum inductance value on the station side. As the inductance isproportional to the number of windings, this is minimum for an antennaL2 consisting of a minimum number of windings. In practice antenna L2comprises a single winding.

On FIG. 4, according to the invention, block 13 described with referenceto FIG. 2 is connected to a filtering device DF able to reject aspectrum band centred around the second frequency F2 equal to 13.56 MHz.This filtering device comprises an inductive element LF and a capacitiveelement CF mounted in parallel between one of the electrodes ofcapacitor C1 and one of the terminals of the inductive station elementL1.

This filtering device DF is a band rejection filter, i.e. a filter whichdoes not transmit frequency F2 and which allows all other frequencies topass, in particular frequency F1 associated with data transmission. Thefiltering device DF behaves as an inductance at frequency F1 and as animpedance of very high value (for example of the order of 20 to 30kOhms) at frequency F2.

This type of filtering is possible because the station comprises aseries arrangement of L1-C1.

According to the invention, the antennae L1 and L2 are approximately ofthe same geometric dimensions. They are superimposed one over the other,which consequently ensures maximum coupling between them.

Under these conditions, the arrangement of antennae L1 and L2 must thenonly meet the needs of the application, i.e. must allow the function ofthe system in a defined zone in order to provide the requiredergonomics.

It is not necessary to apply the portable object in a particulargeometric relation with respect to the station. It is sufficientaccording to the invention merely to apply the card close to the stationantennae.

In practice, the dimensions of antennae L1 and L2 correspond to those ofa rectangle of length 17 cm and width 7 cm. The system thus allows afunctional zone with an area slightly less than the dimensions of thestation antennae.

For example, the remote supply antenna L2 consists of a single windingand antenna L1, dedicated to data transmission consists of approximatelythree contiguous windings. The number of windings of antenna L1 dependson the peak voltage VEX supplied by the generator G1 and thestation-card coupling characteristics. The production technology forantenna L1, in particular the value of the overvoltage coefficient ofthe electronic circuit 3 of the portable object at frequency F1, mustalso be taken into account in determining the number of windings.

The applicant has obtained satisfactory results with the followingnumerical values:

resistive element RC 50 Ohms

capacitive element C1 72 pF

inductive element L1 3.1 μH

inductive element L2 0.4 μH

capacitive element CF 42.1 pF

inductive element LF 3.35 μH

resistive element R1 3 Ohms (part of this resistive element correspondsto the real part of the impedance of antenna L1).

Also, the inductive element LF in parallel with capacitive element CFhas an impedance equivalent to an inductance equal to 4.46 μH atfrequency F1.

FIG. 5 shows the constituent means of the portable object. Here we seethe system dedicated to data transmission described with reference toFIG. 2. According to the invention, it is supplemented with an antennaL4 intended to be coupled electromagnetically to antenna L2 of thestation.

A tuning capacitor C4 at frequency F2 is also provided to form a tunedloop with the inductive station element L2. Such a loop generates at theterminals of antenna L4 an induced alternating supply voltage in thepresence of the magnetic field created by the inductive station elementL2.

Rectifying means RD, for example of the double alternation type, arelinked to the terminals of antenna L4 in order to rectify the inducedalternating supply voltage into a DC supply voltage +VDD intended tosupply the object processing means.

Advantageously, an energy regulation circuit RE is linked to the outputof the rectifying means RD to regulate the induced DC supply voltage asa function of the distance between the station and the portable object.

In practice the energy regulation circuit RE comprises an electronicdevice of parallel regulation type.

To improve the remote supply yield, it is preferable to have a number ofwindings n in antenna L4 of the portable object such that the yield ofthe remote supply system is maximized, and to have a single winding atantenna L2 of the station. It should be noted that the number ofwindings is limited by the technology of the portable object. In orderto reduce the production costs of the portable object, antenna L4 isproduced in the form of windings engraved on a substrate (epoxy glassfor example). The number of windings n is, for example, four for an areaof the portable object of the type described above.

In practice, antenna L4 has a value of 4.1 μH and capacitor C4 a valueof 33.5 pF.

Furthermore, the regulation of the voltage +VDD in the portable objectis associated with the regulation of the current passing through antennaL2 of the station. This regulation is adapted such that the voltagepresent in the terminals of antenna L2 is inversely proportional to thedistance between the station and the portable object. The desired aim isto obtain a reduction in the intensity of the magnetic field emitted byantenna L2 when the portable object approaches antenna L2 of thestation. The solution is obtained via a source G2 dedicated to thesupply which behaves as a current generator.

Clock recovery means RH connected to the terminals of antenna L4 recovera clock signal from the induced alternating supply voltage.

This clock signal is intended to set the timing of the elements 5 of thelogic type or memory type constituting the passive portable object.

Advantageously, this clock recovery eliminates any internal clockdevice, for example of quartz, in the portable object.

It should be noted that the portable object also comprises divider meansDIV linked to the output of the recovery means RH and able to. dividethe frequency of the clock signal thus recovered into a sub-multipleselected to set the timing of the object processing means 5.

A RESET function is available to correctly initialize the logic elementsof the object processing means 5.

Coding means COD and decoding means DEC of the MANCHESTER type are alsoprovided between the object processing means 5 and the electronic datatransmission interface described with reference to FIG. 2 and comprisingthe electronic circuit 3 and the switching means MC and MCA.

The timing of these coding and decoding means is set by the clock signalfrom the divider means.

The antennae L4 and L30 are arranged on the portable object in aparticular geometry.

In the case of a portable object (FIG. 6) of the memory card type ofstandard dimensions, namely 85 mm×54 mm, the remote supply antenna L4is, for example, a rectangle 50 mm×54 mm and the data transmissionantenna L30 is, for example, a rectangle 45 mm×54 mm. Antenna L4therefore overlaps antenna L30 by 10 mm.

The applicant has found that the coupling between these two antennae L4and L30 is disruptive (i.e. generates interference on the data transferfunction) when the overlap exceeds 10 mm.

The material production of the portable object according to theinvention, by elimination of the cell (or battery) and the quartzresonator, has allowed integration of the electronic assembly into asingle silicon chip with the exception of three components which are ofthe miniature capacitor type for elements C4, C30 and a smoothingcapacitor for the supply voltage (not shown).

It should be noted that the fact of providing two independent signals onthe portable object has the advantage of separating, for the productionof the electronic system on the portable object, the energy transfer andclock functions on one side from the data transfer functions on theother.

While a preferred embodiment of the invention has been described above,since variations in the invention will be apparent to those skilled inthe art, the invention should not be construed to the specificembodiment described above.

I claim:
 1. An apparatus for the exchange of information byelectromagnetic coupling between a portable object and a station, inwhich said station comprises:a first generator of a first alternatingvoltage with a first selected frequency, a first resistive stationelement with a first terminal linked to the first generator and a secondterminal, a series arrangement linked to the second terminal and havingat least a first inductive station element, a first capacitive stationelement and a second resistive station element, said arrangement havinga pair of terminals and being able to create a second alternatingvoltage at said terminals, station processing means connected to thefirst and second terminals of the first resistive station element andable to process phase variations between the first and secondalternating voltages, and in which said portable object comprises:anelectronic circuit comprising a first inductive object element and afirst capacitive object element, said circuit being switchable betweenan inactive state and an active state in which it forms a resonantcircuit with the first inductive station element, object processingmeans able to switch the electronic circuit as a function of informationto be transmitted to the station, the phase variation between the firstand second alternating voltages induced by this switching enabling thestation processing means to deduce therefrom said information, whereinsaid station further comprises:a second generator of a third alternatingvoltage of a second selected frequency different from the firstfrequency, wherein the portable object also comprises:a second inductiveobject element independent of the first inductive object element andhaving terminals, a second capacitive object element linked to theterminals of the second inductive object element, said second inductiveobject element being able to form a tuned loop with the second inductivestation element in order to generate at the terminals of the secondinductive object element an inducted alternating supply voltage in thepresence of the magnetic field created by the second inductive stationelement, and wherein the station also comprises a filtering circuit ofdipole type interposed between one of the electrodes of the firstcapacitive station element and one of the terminals of the firstinductive station element, said filtering circuit being able to behaveessentially as an inductance at the first frequency and an impedance ofhigh value at the second frequency.
 2. Apparatus according to claim 1,wherein the filtering circuit comprises an inductive element and acapacitive element mounted in parallel and arranged between the firstcapacitive and inductive elements of the station.
 3. Apparatus accordingto claim 1, wherein the first and second inductive station elements haveapproximately the same geometric dimensions and are superimposed one onthe other.
 4. Apparatus according to claim 3, wherein the secondinductive station element comprises a single winding.
 5. Apparatusaccording to claim 4, wherein the first inductive station elementcomprises approximately three contiguous windings.
 6. Apparatusaccording to claim 1, wherein the portable object further comprisesrectifying means linked to the terminals of the second inductive objectelement and able to rectify the induced alternating supply voltage intoa DC supply voltage intended to supply the object processing means. 7.Apparatus according to claim 6, wherein the portable object furthercomprises an energy regulation circuit linked to the output of therectifying means and able to regulate said DC supply voltage as afunction of the distance between the station and the portable object. 8.Apparatus according to any of the previous claims, wherein the secondgenerator is a current generator.
 9. Apparatus according to claim 7,wherein the portable object further comprises divider means linked tothe output of the clock recovery means and able to divide the frequencyof the recovered clock signal recovered into a sub-multiple selected toset the timing of the object processing means.
 10. Apparatus accordingto claim 1, wherein the portable object further comprises clock recoverymeans linked to the terminals of the second inductive object element andable to recover a clock signal from the induced alternating supplyvoltage.
 11. Apparatus according to claim 1, wherein the station furthercomprises amplifying means able to amplify the third alternating supplyvoltage from the second generator.
 12. Apparatus according to claim 1,wherein second inductive object element comprises n windings, with n aninteger approximately equal to four.
 13. Apparatus according to claim 1,wherein the first and second inductive object elements are arranged inrelation to each other in accordance with a predetermined geometricrelationship intended to limit radio-electric interference. 14.Apparatus according to claim 1, wherein the portable object is a passivecontactless memory card.
 15. Apparatus according to claim 1, wherein theportable object is an electronic label.
 16. A station for the exchangeof information by electromagnetic coupling between the station and aportable object, said station comprising:a first generator of a firstalternating voltage with a first selected frequency, a first resistivestation element with a first terminal linked to the first generator anda second terminal, a series arrangement linked to the second terminaland having at least a first inductive station element, a firstcapacitive station element and a second resistive station element, saidarrangement having a pair of terminals and being able to create a secondalternating voltage at said terminals, station processing meansconnected to the first and second terminals of the first resistivestation element and able to process phase variations between the firstand second alternating voltages, a second generator of a thirdalternating voltage of a second selected frequency different from thefirst frequency, a second inductive station element linked to the secondgenerator, independent of the first inductive station element and ableto create a predetermined magnetic field, and a filtering circuit ofdipole type interposed between one of the electrodes of the firstcapacitive station element and one of the terminals of the firstinductive station element, said filtering circuit being able to behaveessentially as an inductance at the first frequency and an impedance ofhigh value at the second frequency.
 17. A portable object for theexchange of information by electromagnetic coupling between the portableobject and a station, said portable object comprising:an electroniccircuit comprising a first inductive object element and a firstcapacitive object element, said circuit being switchable between aninactive state and an active state, in which it forms a resonant circuitwith the station; object processing means able to switch the electroniccircuit as a function of information to be transmitted to the station,the phase variation between two alternating voltages at a first selectedfrequency of the station induced by this switching enabling the stationto deduce therefrom said information; a second inductive object elementindependent of the first inductive object element and having terminals;and a second capacitive object element linked to the terminals of thesecond inductive object element, said second inductive object elementbeing able to form a tuned loop with the station in order to generate atthe terminals of the second inductive object element an inducedalternating supply voltage at a second selected frequency different fromthe first frequency in the presence of a magnetic field created by thestation.